Discovery of a Very Young Field L Dwarf, 2MASS J01415823–4633574
Discovery of a Very Young Field L Dwarf, 2MASS J01415823–4633574
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发现一颗非常年轻的L型矮星，2MASS J01415823–4633574
DOI：
10.1086/499622
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
P. Lowrance
中科院分区：
文献类型：
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作者：
J. Kirkpatrick;T. Barman;A. Burgasser;M. R. Mcgovern;I. McLean;C. Tinney;P. Lowrance
在跟踪从两微米全天测量中以光度方式挑选的L矮星候选者时，我们发现了一个不寻常的天体，命名为2MASS J01415823-4633574。它的光谱显示出非常强的氧化钒谱带，但氧化钛、钾和钠的吸收异常弱。在形态上，这种光谱特征介于老场早期的L矮星[log(G)≈5]和很晚的M巨星[log(G)≈0]之间，这使得我们倾向于用低重力来解释这颗L矮星独特的光谱特征。只有当这颗L矮星的质量比一颗典型的类似温度的老场L矮星低得多，并且仍在收缩到它的最终半径时，这种低重力才能解释。这些情况意味着他们的年龄很小。在近红外光谱中还发现了年轻的进一步证据，包括一个三角形的H波段连续体，这让人想起在猎户座星云星团中发现的年轻的棕矮星候选者。利用上述信息，再加上与棕矮星大气和内部模型的比较，我们目前最好的估计是这颗L矮星的年龄为1-50Myr，质量为6-25MJ。尽管没有检测到锂(伪等宽)似乎与其他年轻证据相矛盾，但我们认为，锂在较低重力下会变得更弱，就像所有其他碱性线一样，因此在被用作这一体制下物体的年龄或质量诊断之前，需要仔细考虑。2MAS0141-4633在天空中的位置，加上距离估计为~35pc，上述年龄估计表明，该天体可能是30 Myr古老的图卡纳/Horologium协会或~12 Myr古老的βPic运动群的棕矮星成员。通过三角视差确定的距离(正在进行中)和整个空间运动的测量需要用来检验这一假设。
While following up L dwarf candidates selected photometrically from the Two Micron All Sky Survey, we uncovered an unusual object designated 2MASS J01415823-4633574. Its optical spectrum exhibits very strong bands of vanadium oxide but abnormally weak absorptions by titanium oxide, potassium, and sodium. Morphologically, such spectroscopic characteristics fall intermediate between old field early-L dwarfs [log(g) ≈ 5] and very late M giants [log(g) ≈ 0], leading us to favor low gravity as the explanation for the unique spectral signatures of this L dwarf. Such a low gravity can be explained only if this L dwarf is much lower in mass than a typical old field L dwarf of similar temperature and is still contracting to its final radius. These conditions imply a very young age. Further evidence of youth is found in the near-infrared spectrum, including a triangular-shaped H-band continuum, reminiscent of young brown dwarf candidates discovered in the Orion Nebula Cluster. Using the above information along with comparisons to brown dwarf atmospheric and interior models, our current best estimate is that this L dwarf has an age of 1-50 Myr and a mass of 6-25MJ. Although the lack of a lithium detection (pseudo-equivalent width <1 Å) might appear to contradict other evidence of youth, we suggest that lithium becomes weaker at lower gravity like all other alkali lines and thus needs to be carefully considered before being used as a diagnostic of age or mass for objects in this regime. The location of 2MASS 0141-4633 on the sky coupled with a distance estimate of ~35 pc and the above age estimate suggests that this object may be a brown dwarf member of either the 30 Myr old Tucana/Horologium association or the ~12 Myr old β Pic moving group. Distance as determined through trigonometric parallax (underway) and a measure of the total space motion are needed to test this hypothesis.